Starting in 1908s, the optical measurement technology explored by the mechanical system with potentiometer as the human body joint angle measurement and the use of active tag opens up the research using the computer in the human body capture, and the mechanical and optical dynamic capture technology and equipment have gradually been developed. Then, the dynamic capture technology has attracted more and more attentions from the researchers and developers alike, as well as developed from the initial academic study gradually to the commercial realization. One of the important applications of the dynamic capture technology development is to be able to better capture the human body dynamic data to provide to the animation, film and television and other multimedia industries, to describe the near-real movement state to reduce production costs, as well as greatly enhance the production efficiency to achieve the entertainment effect, which is still the major commercial application for dynamic capture technology.
The conventional dynamic capture technology can be broadly divided into mechanical-based technology and optical-based technology; wherein the mechanical-based technology is for a user to wear a mechanical frame attached with encoder to record the rotation of the joints of the arm when the user moves the arm so as to learn the rotation of the arm joint movement. The advantage of this approach is the measured angle can be easily converted to the input required by the motor when applied to the humanoid robot arm. In contrast, optical-based dynamic capture technology is to use cameras disposed at different angles to track the marks placed on the subject, and then feed the tracking information back to the computer for a large and complex computation to learn the dynamic state of the target. In particular, since the 1980s after the rapid development of optical-based dynamic capture technology, the optical-based technology has been the mainstream choice in the market due to high precision characteristics. On the other hand, the shortcomings of optical dynamic capture technologies are that the range of motion of the subject must often be confined to a fixed range; otherwise the line-of-sight might be shielded.
However, with the micro-electro-mechanical system (MEMS) technology breakthroughs and the rise of related industries, an approach to use inertial measurement unit (IMU) for dynamic data capture has emerged. In general, the IMU includes three kinds of sensors, that is, an accelerator, a gyroscope and a magnetometer. The chip is not only small in size but also low in price, which constitutes a major feature of the technology. The principle of IMU-based dynamic capture technology is the application of IMU to obtain the acceleration, angular velocity and magnetic field strength information, which is processed by an algorithm to obtain the pose of the object in the space. Therefore, the processing of the acceleration, angular velocity and magnetic field strength information becomes extremely important when using this approach. The main reason is that the angular velocity measured by the gyroscope, even in the state where the entire IMU remains stationary, still has a certain degree of offset error, and the error will be accumulated after the integral operation in the algorithm. On the other hand, the magnetometer is also easily susceptible to the effects of the ferromagnetic environment, which in turn causes the read value to cause the offset. These are the natural defects that are unavoidable in the IMU. Regardless, from the perspective of volume, precision, cost, and immediacy, the IMU-based approach is still more appropriate than the mechanical-based or optical-based technologies when applied to measuring the pose of small objects in space.
With improved resolution precision of the dynamic capture system of human motion, the feasibility of using the technology as the measurement system significantly increases; therefore, the dynamic capture technology begins to extend to other application areas than only to entertainment, including medical rehabilitation, ergonomics, virtual reality, and industrial measurement and other fields. Relatively, the more and more widely application areas also place higher demands regarding resolution precision on the dynamic capture technology, which becomes an important issue on whether the industry can achieve successful commercialization.